Gas shut-off system

ABSTRACT

This gas shut-off system includes a flow rate sensor (2) for detecting a gas flow rate and a control unit having a miocrocomputer (6) which determines abnormal states such as gas leak when a predetermined flow rate continuously keeps over a predetermined time period and automatically closes a shut-off valve (4) in accordance with the determination. A battery (13) is employed as a power-source for the microcomputer (16) and the shut-off valve (4). In order that the consumption amount of the battery (13) is reduced as small as possible, the microcomputer has a standby function and is set to the standby condition except gas flow rate computation and so on until the shut-off valve (4) is opened after set to the shut-off condition. An indicating device for indicating various states of the system comprises a light emitting diode (19) which is single indicator, so that power consumption is reduced.

TECHNICAL FIELD

The present invention relates to a gas shut-off system for prevention ofexplosive accidents caused by town gas, liquefied petroleum gas, and thelike, and in particular to a gas shut-off system comprising a controlunit including a microcomputer whereby a shut-off valve is automaticallyclosed in response to detection of abnormal conditions such as gas leakwhich is made by the aid of a gas flow rate sensor, and using a batteryas a power supply.

TECHNICAL BACKGROUND

Town gas and LP gas are being widely used as an energy source forcooking, heating, hot-water supply, or the like. However, if there isany failure of handling, these gases explode and cause a great accident.On the other hand, recently high altitude and airtight houses havecaused the neighborhood to suffer damage from the gas accident.Therefore, putting the safety provision and gas device for prevention ofthe gas accidents to practical use should be early achieved in view ofsocial conditions.

For prevention of the gas accidents, fuse cocks, reinforced gas hoses,town gas alarm devices, shut-off systems associated with alarm devices,and the like have been hitherto employed. These have not been spread toexisting houses because of troublesome installation and are notnecessarily effective for explosive accidents with suicidal intent whichaccount for most of the accidents.

Of the causes of gas accidents, short-time great amount discharge of rawgas resulting from the separation of a pipe from a gas cock or theintentional opening of a gas cock and abnormal heating or oxygendeficiency resulting from the forgetting of turning-off of gas equipmentimportant factors for the accidents, the accidents with suicidal intentrelating to the former.

In these accidents, the flow rate pattern such as that gas flow rate andcontinuous time of flow rate becomes abnormal as compared with thenormal conditions. Therefore, it is possible to prevent a wide range ofgas accident including the accident with suicidal intent byautomatically shutting off the gas main when the gas flow rate patternbecomes abnormal. Furthermore, the installation can be improved bycombining the system therefor with a gas meter.

The estimation of pattern of use, comparison with an abnormal pattern,and the like can be realized by means of a microcomputer.

DISCLOSURE OF THE INVENTION

An object of the present invention is particularly to provide along-life use for a battery used as a power supply in a system forpreviously preventing explosive accidents caused by gas such as town gasand LP gas used as an energy source for cooking, heating, hot-watersupply in a house. A gas shut-off system according to the presentinvention includes a microcomputer programmed in terms of, for example,explosive limit to shut off the discharging of gas before the occurrenceof gas explosion by the computation based on gas flow rate and dischargetime. Also included in view of workability is a battery as a powersource. Therefore, a gas shut-off system according to the presentinvention is arranged to minimize the consumption of the battery and toprovide a long-time use of the battery.

In this system, a gas flow rate is detected by a flow rate sensor, and amicrocomputer determines whether the flow rate pattern is normal orabnormal on the basis of the detection of the gas flow rate and actuatesa shut-off valve to shut off the gas in response to the determination ofabnormality. This system has greater ability for prevention of accidentsas compared with conventional gas-accident preventing countermeasures.In addition, the system is combined with the gas meter, resulting inmaking it easy to install into existing houses and improving theworkability.

This system comprises a lithium battery having excellent long-timereliability as a power source, a flow rate sensor having a reed switch,an exclusive CMOS 4-bit 1-chip microcomputer in which the consumption ofcurrent is low, an indicator including a LED and having an excellentvisibility, and a self-hold type shut-off valve which matches thecharacteristics of the lithium battery. The arrangement enables thesystem to be operated by one lithium battery over ten years.

The reason that a battery has been selected as a power source of thissystem is as follows. Namely, in the case of use of the commercialpower, it is required to provide a power cord between a power line and agas meter, resulting in complex work and unsuitability for existinghouses. Furthermore, when the power cord is intentionally oraccidentally cut or when the supply of power to this system is stoppeddue to service interruption and the like, this system becomesinoperative. Therefore, a system including a battery as a power sourcemust be required.

However, the duration of service of the battery is limited and thereforeit is required to exchange the battery with a new one when the voltageis dropped due to consumption. Period of the battery exchange as long aspossible is desirable for user because of reduction of labor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a gas shut-off system according to anembodiment of the present invention;

FIG. 2 is a detailed circuit diagram of FIG. 1 arrangement;

FIG. 3 is a diagram showing the microcomputer of FIG. 2 circuit;

FIGS. 4 and 5 are wave form charts for understanding the operation ofthe circuit of FIG. 2;

FIG. 6 is a wave form chart for understanding the operation of anindicator;

FIG. 7 is a diagram illustrating a gas shut-off system according toanother embodiment of the present invention;

FIG. 8 is a diagram showing a gas shut-off system according to a furtherembodiment of the present invention;

FIG. 9 is wave form chart for undestanding the operation of the systemof FIG. 8; and

FIG. 10 is a diagram illustrating a gas shut-off system according to astill further embodiment of the present invention.

MOST PREFERRED EMBOIDMENTS OF THE INVENTION

An embodiment of the present invention will be hereinbelow describedwith reference to the drawings.

A flow rate sensor 2 for measuring a flow rate is mounted on a gas meter1 as shown in FIG. 1. A signal from the flow rate sensor 2 is applied toa control unit 3 for performing the determination of gas shut-off. Thecontrol unit 3 computes a gas flow rate and generates a gas shut-offsignal when the gas flow rate meets predetermined conditions in terms ofan abnormal flow rate. In response to the gas shut-off signal, ashut-off valve 4 provided in a gas passage is actuated to close the gaspassage. Furthermore, the control unit 3 is responsive to signals fromabnormality sensors such as earthquake sensor and CO sensor to generatethe shut-off signal to shut off the gas passage when predeterminedconditions are satisfied.

The control unit 3 includes a microcomputer programmed to effect thedetermination of the gas shut-off, the microcomuputer generating ashut-off signal to close the shut-off valve 4 when gas continuouslyflows for a predetermined time period. Namely, in the case of abnormallygreat flow rate, the shut-off signal is generated during a short time,whereas even if the flow rate is small, the determination of gas leak ismade when the flow rate is not varied over a long time and the shut-offsignal is generated, so that the discharge of gas is automaticallystopped before reaching the explosive limit even if a closed space isfilled with gas. This is effective for the abnormal condition that rawgas is continuously discharged with the cock of a gas device provided ina room being opened.

Furthermore, an earthquake sensor is effective as means for preventingthe leak of raw gas and explosive accident caused by the damage of thegas passage provided at downstream of the gas meter 1 or the connectingportion between the gas passage and the gas device due to earthquake,while a CO sensor is effective as means for detecting the permeation ofcarbon monoxide (CO) in a room due to incomplete combustion of a gasapparatus. These sensors are provided as an abnormality sensor.

The microcomputer of the control unit 3 can be set to a standby mode.The standby mode means the condition that the microcomputer waits for aspecific signal, i.e., interruption signal. When the signal is receivedin the condition, it returns to a normal operating condition (operatingmode). Generally, current required when the microcomputer is in thestandby mode is several percents of current required in the operatingmode, the value of the current being small. The reason is that most offunctions are stopped in the standby mode.

The control unit 3 receives an output of the flow rate sensor 2 arrangedto count the reciprocating movements of the diaphragm of the gas meterand determines whether or not the gas flow rate periodically read iscoincident with the gas aptitude use condition previously programmed. Ifthe gas flow rate is coincident with the aptitude use condition, themeasurement of flow rate is subsequently made. On the other hand, if itdoes not agree therewith because of abnormality, a gas shut-off signalis generated to shut off the shut-off valve 4. The comparison of the gasflow rate and the gas aptitude use condition is made for an extremelyshort time, and the microcomputer is in the standby mode except thiscomparison process, preventing excess battery consumption.

The circuit including the control unit 3 is shown in detail in FIG. 2.

A flow rate signal from the flow rate sensor 2 provided in the gas meter1 is inputted through an interruption input terminal iNT1 to themicrocomputer 6 of the control unit 3. A signal indicative ofabnormality from the abnormality sensor 5 is supplied through anabnormality sensor processing circuit 7, an OR gate 11, and an interruptinput terminal iNT2 to the microcomputer 6. The abnormality sensorprecessing circuit 7 comprises, for example, a chattering absorptioncircuit if the abnormality sensor 5 has a contact output. The shut-offoutput is applied from an output terminal o1 through a shut-off valvedriver 8 to the shut-off valve 4. The reference numeral 9 represents areturn signal detecting circuit for detecting a return signal when theshut-off valve 4 is manually opened after the shut-off. Since a battery13 is used as a system power source, a valve of one-shot self-hold typein which electromagnetic energy is not required for maintaining the theopening and closing conditions is employed as the shut-off valve 4.

In order that the shut-off valve 4 is of the one-shot self-hold type,for example, magnetic force of a permanent magnet is used formaintaining the shut-off valve 4 opening, and for setting the same toclose a one-shot current is applied to an electromagnetic coil so as togenerate the magnetic force having inverse polarity to the polarity ofthe permanent magnet and the shut-off valve 4 is set to the closedcondition by means of both the electromagnetic force and the force of aspring and then maintained closed by spring force. Setting the sameagain to the opening condition is achieved by an external force such asmanual force. At this time, the electromagnetic coil generatescounter-electromotive force. Therefore, this counter-electromotive forcedeveloped across the electromagnetic coil of the shut-off valve can beused as the return signal. When this counter-electromotive force isapplied to a junction type N channel FET 10 making up the return signaldetecting circuit 10, this FET 10 becomes OFF during the time periodthat the counter-electromotive force is below cut-off voltage. Theoutput of the return signal detecting circuit 9 is supplied through theOR circuit 11 and the input terminal iNT2 to the microcomputer 6 andtherefore only one OR circuit 11 can be used as a logic circuit. Thereference numeral 19 represents a light emitting diode which is one kindof indicators for indicating that the shut-off valve 4 is in theshut-off condition, only one diode being used. The light emitting diode19 is controlled through an output terminal o5 of the microcomputer 6.

The operation made in accordance with such an arrangement will bedescribed hereinbelow.

When the shut-off valve 4 is set to the opening condition, the firstoutput terminal o3 of the microcomputer 6 is set to a high level and theabnormality sensor processing circuit 7 is in the operating condition,while the second output terminal o4 is set to a low level and the returnsignal detecting circuit 9 is in the non-operating condition. In theseconditions, only an abnormality signal of the abnormality sensor 5 isinputted through the abnormality sensor processing circuit 7 and the ORgate 11 to the input terminal iNT2. When the shut-off valve 4 is closedin response to the occurrence of abnormality, the first output terminalo3 of the microcomputer 6 becomes low level and the second outputterminal o4 becomes high level, whereas the abnormality sensorprocessing circuit 7 is set to the non-operating condition and thereturn signal detecting circuit 9 is set to the operating condition. Inresponse to the return of the shut-off valve 4, its electromagnetic coilgenerates a counter-electromotive force, and when thecounter-electromotive force is less than the cut-off voltage of the FET10, the FET 10 is set to the off condition and its drain voltage becomeshigh level which is in turn applied through the OR gate 11 to the inputterminal iNT2.

FIG. 3 is an illustration of the arrangement of the microcomputer 6. Themicrocomputer 6 has a standby mode as described above and the standbycontrol is performed as follows.

A stop command from a CPU stops the operation of a system clockgenerator 21, and therefore the system clock φ is stopped and themicrocomputer 6 is set to the standby mode. Thereafter, in response tothe application of an interrupt signal through the input terminal iNT2,the system clock generator 21 is again energized so that themicrocomputer is returned to the operating mode. The power-supplycurrent (I_(DD)) in the standby mode is several percents of the currentconsumed in the operating mode, this being very small.

A timer 14 comprises a generator for oscillating a crystal 12, a dividerfor dividing the frequency of the generator, and a counter for countingtime-base signals produced by the divider.

FIG. 4 is a timing chart in terms of the circuit of FIG. 2. This timingchart represents the condition that the shut-off valve 4 is closed inresponse to the flow rate sensor 2 detcting that the gas flow becomesmore than a predetermined flow rate.

Before a time tφ, the shut-off valve 4 is not closed and therefore anoutput terminal o2 of the microcomputer 6 is a low level (Lo) and theflow rate sensor 2 is set to the active condition. The output of theoutput terminal o3 thereof is Hi, the output of the output terminal o4is Lo, the abnormality sensor processing circuit 7 is set to the activecondition, and the return signal detecting circuit 9 is set to theinhibited condition. These conditions are maintained until the shut-offof the shut-off valve 4.

In response to the flow of gas, the flow rate sensor 2 is turned on andoff in accordance with the gas flow rate. When the flow rate sensor isturned on at the time tφ, the input signal to the input terminal iNT1 ofthe microcomputer 6 is changed from Lo to Hi and the microcomputer 6allows an interrupt to occur in response to the positive edge, andtherefore the microcomputer is transferred from the standby mode to theoperating mode. The microcomputer measures the time Tφ between theprevious iNT1 interrupt and the present interrupt by means of a timerand then compares the measured time Tφ with a shut-off condition T_(F)previously stored in a ROM. When Tφ>T_(F), determination is made whereinthe gas flow rate is small and no shut-off is performed. The timer 14 isagain energized and "STOP" command is again executed to be set tostandby mode. The above processes take a time T_(ON), and hereaftersimilar operations will be effected whenever the input terminal iNT1interrupt occurs. At a time t2, the flow rate sensor is set from on tooff and the input of the input terminal iNT1 of the microcomputer 6 isvaried from Hi to Lo. However, this negative edge results in nointerrupt. At a time t3, the flow rate sensor is set from off to on andtherefore interrupt occurs. Although the microcomputer 6 again makes theoperating mode, because of T1>T_(F), it is further set to the standbycondition. Thereafter, when the gas flow rate is abnormally increased,the on and off of the flow rate sensor 2 become shorter. This isdetected by the microcomputer 6 set to the operating mode at a time t4.In this case, the determination is made as T2<T_(F) and therefore themicrocomputer generates a shut-off signal through the output terminal o1by a time period T_(OFF). When the generation of the shut-off signal isterminated at a time t5, the output of the output terminal o2 is set toHi, the output of the output terminal o3 is set to Lo, the inputterminal iNT1 input from the flow rate sensor 2 is set to inhibitedcondition, and the abnormality sensor processing circuit 7 is set toinhibited condition. After the termination of these processes, at a timet6, the outout terminal o4 is set to Hi and the return signal detectingcircuit 9 is set to the active condition. The reason that theseprocesses is not performed at the time t5 but performed at the time t6elapsed by an appropriate time from the time t5, is to prevent acounter-electromotive force (negative voltage) produced at the time t5by the turning-off of current passing through the coil of the shut-offvalve from being detected as a return signal. Thereafter, themicrocomputer 6 is set to the standby mode and then waits for aninterrupt input (iNT2) from the return signal detecting circuit 9.

When the shut-off valve is manually opened at a time t7, acounter-electromotive force (negative voltage) is developed in the coilof the shut-off valve. The FET 10 is turned off by the negative voltageand therefore a positive edge from Lo to Hi is inputted to the inputterminal iNT2 of the microcomputer. Thereby, the microcomputer 6 is setto the operating mode, confirms that the shut-off valve 4 has beenopened, and returns the outputs of the output terminals o2, o3, and o4to the conditions before the shut-off (before the time t4) at a time t8.Thereafter, the microcomputer 6 is set to the standby mode and waits foran interruption input (iNT1) from the flow rate sensor or an interruptinput (iNT2) from the abnormality sensor.

An output terminal o5 of the microcomputer 6 generates a signal forturning on and off the light emitting diode 19 after the time t6, thatis, when the shut-off valve 4 is set to the closed condition. Theturning on and off mode is employed for reducing the consumption of thebattery for indication. Namely, if the duty for the lighting is 1/100,the average current consumption also becomes 1/100. This can be easilyrealized by, for example, lighting it by 16 msec at intervals of 1.6second. Such an indication is easily visible. When a return signal isinputted at the time t7, the microcomputer 6 outputs a lighting signalfrom the output terminal o5 by a time period longer than the lightingtime (for example, 1 sec in the case of the lighting time of 16 msec),so that the fact that the return signal is inputted to the microcomputer6 is indicated to the exterior. This is performed to indicate that thereturn operation has been accurately effected.

FIG. 5 is a timing chart for understanding the conditions that theabnormality sensor 5 of FIG. 2 circuit is energized.

When abnormality has been detected by the abnormality sensor 5, thedetection signal is inputted as an interruption signal to the inputterminal iNT2 (time 12). In this case, the microcomputer is set from thestandby mode to the operating mode to check a signal supplied to theinput terminal iNT2. The shut-off condition that the shut-off isperformed when abnormal state is continued over a predetermined timeT_(A) is stored in a ROM of the microcomputer 6. At a time t13, sincethe abnormal state has been continued by the predetermined time T_(A),the microcomputer 6 outputs a time T_(OFF) shut-off signal from theoutput terminal o1. The operations after the time 13 are similar to theoperations after the time t4 in FIG. 4.

Here, a detailed description is made in terms of the indication by thelight emitting diode 19. Only one light emitting diode is used forindicating the shut-off and return. The shut-off is indicated by turningon and off the diode, while the return of the shut-off valve isindicated by lighting the same for a long time. The shut-off, asindicated in FIGS. 3 and 4, is roughly divided into shut-off caused byflow rate and shut-off caused by the abnormality sensor. Because theshut-off cause is different, it is desirable that the shut-off cause canbe estimated in accordance with the indication. Therefore, theturning-on and off pattern for indicating the shut-off condition is madeas shown in FIG. 6, for example. In FIG. 6, the reference character arepresents the turning on and off pattern of the shut-off caused by flowrate and character b designates the pattern of the shut-off caused bythe abnormality sensors. Such variations of the turning-on and offpattern can be easily realized in accordance with the program of themicrocomputer 6. In FIG. 6, in any cases, one lighting is performed atevery period T_(L) and the average currents required for the indicationare equal to each other.

Now, a light emitting diode which has one package and enables to emitdifferent two colors (generally, red and green) is available. If thediode is used, the output of the microcomputer 6 is increased by oneand, in accordance with the pattern of FIG. 6b, when the shut-off iscaused by flow rate, the indication can be made with green, and when itis caused by the abnormality sensor, the indication can be made withred.

With the shut-off valve 4 being opened, only when the flow rate sensor 2is varied from off to on and the abnormality sensor 5 detectsabnormality, the microcomputer 6 is set to the operating mode.Furthermore, even if it is in the operating condition, after thetermination of predetermined processes, it is again returned to thestandby mode. Therefore, the time period T_(S) set to the standby modeis longer than the time period T_(ON) set to the operating condition.The average current I_(DD) is expressed as follows. ##EQU1## where:I_(DS) =power-supply current in standby mode

I_(DR) =power-supply current in operating mode

For example, when ##EQU2## It will be seen from the above equation thatthe current I_(DD) is about 1/5 as compared with I_(DR) in the operatingmode. Therefore, using the same battery, the operating time periodbecomes five times. Furthermore, the FET 10 of the return signaldetecting circuit 9 is set to the on condition because the voltagebetween its drain and gate is zero, and current does not flow betweenits drain and source because the output of the output terminal o4 is Lo,resulting in prevention of useless consumption. The reason is that it isnot required to detect the return because the shut-off valve 4 is in theopening condition.

On the other hand, with the shut-off valve 4 being closed, the output ofthe output terminal o2 of the microcomputer 6 is Hi and the output ofthe output terminal o3 thereof is Lo, and therefore even if the flowrate sensor is turned on or the abnormality sensor 5 is set to abnormalcondition, current does not flow through them, resulting in nouselessness.

In addition, because the light emitting diode 19 is turned on and off,it is possible to reduce the average consumed current as compared withlighting.

FIG. 7 illustrates another embodiment of the present invention. A logiccircuit 15 receives a signal from the abnormality sensor 5 through theabnormality sensor processing circuit 7 when the shut-off valve 4 isopened and then inputs the signal through the input terminal iNT2 to themicrocomputer 6. On the other hand, when the shut-off valve 4 is closed,a return signal from a return signal generating section 16 comprising areed switch and so on is inputted through a return signal processingcircuit 20 to the microcomputer 6. In the embodiment of FIG. 2, theoutputs of the output terminals o3, o4 of the microcomputer 6 controlsthe abnormality sensor processing circuit 7 and the power supply of thereturn signal detecting circuit 9. However, in the embodiment of FIG. 6,the gate of the logic circuit 15 is controlled. That is, when theshut-off valve 4 is opened, the output of the output terminal o3 of themicrocomputer 6 is Hi, the output of the output terminal o4 thereof isLo, an AND gate 15A is set to active condition, an AND gate 15B is setto inhibited condition, and the output of the abnormality sensorprocessing circuit 7 is inputted to the input terminal iNT2 of themicrocomputer 6. Furthermore, when the shut-off valve 4 is closed, theoutputs of the output terminals o3, o4 of the microcomputer 6 becomeinverse, the AND gate 15A is set to the inhibited condition, the ANDgate 15B is set to the active condition, and the return signal isinputted to the input terminal iNT2.

A further embodiment of the present invention will be descrived withreference to FIG. 8. FIG. 8 arrangement does not include theabove-described abnormality sensor 5. A control unit 3 includes amicrocomputer 6 having a standby mode function. The microcomputer 6 isswitched from the operating mode to the standby mode in accordance witha software. Here, The operating mode means the condition that themicrocomputer 6 is normally operated, and in this case all functions areset to the operating conditions. On the other hand, since the functionsare almost set to the stop condition in the standby mode, the consumedcurrent is reduced to about several percents of that of the operatingmode. After the microcomputer 6 is once set to the standby mode, itmaintains the standby mode until a return signal from a return signalgenerating section 16 is inputted to its interrupt input terminal iNT2.In response to the input, the microcomputer is again set to theoperating mode. Namely, as shown in FIG. 9, when the microcomputer 6 isin the operating mode, a shut-off signal is generated at a time t1. Whenthe shut-off valve 4 is set to the closed condition at a time t2, thereturn signal generating section 16 is switched from on to off. Whentime goes to t3, that is, a predetermined time period is elapsed fromthe time t1, the generation of the shut-off signal is stopped.Thereafter, the microcomputer 6 is switched from the operating mode tothe standby mode at a time t4. When the shut-off valve is set to theopened condition at a time t5, the return signal generating section 16is set to on and a return signal is inputted to the interruption inputterminal iNT2 of the microcomputer 6, and therefore the microcomputer 6is again switched from the standby mode to the operating mode to startto read a signal from the flow rate sensor 2.

A still further embodiment of the present invention will be describedwith reference to FIG. 10. In FIG. 10 arrangement, the disconnection ofthe shut-off valve 4 can be detected.

In FIG. 10, the reference numeral 13 represents a battery and the on andoff of a reed switch of a flow rate sensor 2 are converted into Hi andLo voltage signals which are in turn inputted to the input terminal iNT1of the microcomputer 6. Numeral 16 designates a return signal generatingsection (which uses a reed switch), and a return signal processingcircuit 20 converts the on and off of the reed switch 16 into Hi and Lovoltage signals and inputs them to an input terminal iNT3 of themicrocomputer 6. In the shut-off condition, the reed switch 16 is offand the output of the return signal processing circuit 20 is Lo. Numeral17 represents a disconnection detecting section which has a transistor18.

The microcomputer 6 receives a signal from the flow rate sensor 2,processes the signal in accordance with a predetermined processprocedure, and checks whether or not the shut-off should be performed.If the shut-off condition is satisfied, a shut-off signal is outputtedfrom the output terminal o1 to a shut-off valve driver 8. In the processprocedure, for example, it is performed to check whether or not the flowrate detected by the flow rate sensor 2 keeps a constant value over apredetermined time period. If it is over, the used time is longer thanthe normal use time of the equipment corresponding to the flow rate andsuch a condition is considered as an abnormality, and therefore ashut-off signal is outputted for a required time period. In the shut-offcondition, since the reed switch 16 of the return signal generatingsection is off, the input terminal iNT3 is set to Lo. Next, when theshut-off valve 4 is manually opened, the reed switch 16 of the returnsignal generating section is turned on and the output of the returnsignal processing circuit 20 becomes Hi, and thereby the microcomputer 6can know the fact that the shut-off valve 4 has been set to the openedcondition. The Hi signal is outputted periodically (for example, every24 hours) from the output terminal o2 to energize the disconnectiondetecting section 17. This is performed using the internal timer 14(FIG. 3) of the microcomputer 6. The output time period of the Hi signalis established so as not to operate the shut-off valve 4. When theoutput of the output terminal o2 becomes Hi, voltage is applied to theemitter of the transistor 18. If the electromagentic coil of theshut-off valve 4 is normal without disconnection, a base current Ibflows so that the transistor 18 is turned on. Therefore, the collectorvoltage Ec of the transistor 18 becomes Hi and is inputted to an inputterminal i2 of the microcomputer 6. The microcomputer 6 can check thepresence or absence of the disconnection of the electromagnetic coil ofthe shut-off valve 4 by receiving the condition of the input terminalport i2 when Hi signal is outputted through the output terminal o2. Ifthe electromagnetic coil of the shut-off valve 4 is normal, the Hisignal is inputted. If there is a disconnection, the Lo signal isinputted. When disconnected, a turning-on-and-off signal is outputtedfrom the microcomputer 6 to an indicating section (light emitting diode19) to inform an user. In this case, the turning on and off period isshortened to make possible to easily distinguish this turning on and offindication from the turning on and off indication at the time ofshut-off.

INDUSTRIAL APPLICABILITY

As understood from the above, the present invention relates to a systemwhich is more for prevention of gas accidents such as gas explosionresulting from the separation of a rubber tube from a gas cock and theintentional opening of a gas cock and a fire and oxygen deficiencyresulting from the forgetting of turning-off of gas equipment, ascompared with conventional countermeasures.

Furthermore, the system is combined with a gas meter and uses a batteryhaving long time reliability as a power source. Therefore, it ispossible to maintain high reliability for a long time and to be employedfor existing houses.

What is claimed is:
 1. A gas shut-off system powered by a battery,comprising:flow rate measuring means provided in a gas passage formeasuring a gas flow rate therein to generate a signal indicative of themeasured gas flow rate; shut-off means provided in said gas passage toallow shutting off the flow of gas, said shut-off means generating areturn signal when being set to the opening condition; and a controlunit coupled to said flow rate measuring means and said shut-off meansand arranged to assume an operating mode and a standby mode, saidcontrol unit having mode switching means whereby said control unit isallowed to be switched from said standby mode to said operating mode andstoring data representative of a proper use condition of gas, saidcontrol unit determining a use state of gas on the basis of the flowrate signal from said flow rate measuring means and further determiningan abnormality when the use state departs from the proper use conditionand outputting a shut-off signal to said shut-off means in response tothe determination of abnormality, said control unit switching by itselfto said standby mode after the output of said shut-off signal and beingthen switched from said standby mode to said operating mode in responseto an input of said return signal to said mode switching means.
 2. A gasshut-off system as claimed in claim 1, further comprising indicatingmeans for indicating a plurality of different states of the system witha plurality of turning-on-and-off patterns, said indicating means usingone indicator, and said indicating means informs a state to the exteriorwith a first pattern indicated when a gas shut-off is performed and asecond pattern indicated when said shut-off means is returned to theopening state.
 3. A gas shut-off system as claimed in claim 1, furthercomprising an abnormality sensor for detecting abnormalities such asearthquake and discharge of CO gas and generating an abnormality signalin response to the detection, and wherein said control unit isresponsive to said abnormality signal to generate said shut-off signalso that said shut-off means is set to the closing state to shut off theflow of the gas.
 4. A shut-off system as claimed in claim 1, whereinsaid shut-off means comprises an electromagnetic coil, and furthercomprising disconnection detecting means for detecting a disconnectionof said electromagnetic coil by flowing a current through saidelectromagnetic coil.
 5. A shut-off system as claimed in claim 4,wherein a flowing time period of the current for the detection of thedisconnection thereof is shortened as compared with that of saidshut-off signal and the current is periodically supplied to saidelectromagnetic coil, and further indicating means for indicating thedisconnection of said electromagnetic coil.